1. Field of the Invention
The present invention relates to a mounting terminal substrate having a mounting terminal provided on a substrate and a display device using the substrate, for example, a mounting terminal substrate which can be appropriately utilized for a liquid-crystal display device.
2. Description of the Related Art
A liquid-crystal display device is thin, light weight, and power-thrifty and used as display devices of many pieces of equipment. A chip-on glass (COG) mounting technique for mounting a driver IC for the purpose of driving liquid-crystal directly on a glass substrate on which are formed mounting terminals is frequently used for middle-size and small-size liquid-crystal display devices. In COG mounting, electrical conduction is often established between the mounting terminals and the driver IC by way of an anisotropic conductive film (ACF). In the ACF, conductive particles produced by coating resin balls with Au or Ni are dispersed into an insulative thermosetting adhesive. Protruding electrodes (hereinafter called “bumps”) made from Au, or the like, are formed in the terminal of the driver IC. In COG mounting, opening sections in the mounting terminal, from which an insulation film for protecting wiring or a mounting terminal area has been partially removed, are aligned to the bumps, and the substrate is subjected to thermo-compression bonding, whereby electrical conduction is established by way of the conductive particles (e.g., JP-A-2002-196703). Moreover, TAB mounting is often used for a large-size liquid-crystal display device, wherein a mounting terminal formed in line on a glass substrate is mounted on a tape automated bonding (TAB) corresponding to a wiring film substrate on which is mounted a driver IC byway of an ACF (e.g., JP-A-9-90397).
Recently, in a small-size liquid-crystal display device for use with a portable device, a pixel (dot) pitch becomes smaller to a size of the order of 40 μm to 60 μm in association with an increase in resolution. TAB mounting encounters difficulty at such a narrow pitch. In order to address the tendency toward a narrower pitch among mounting terminals, there has been practiced COG mounting in which mounting terminals are staggered in two rows to make the terminal pitch double a wiring pitch. However, in the case of a staggered arrangement, mounting terminals arranged at a narrow pitch has a terminal pitch of about 35 μm.
In association with narrowing of a pitch in the direction of a row where a plurality of mounting terminals are arranged, the width of an opening section in the insulation film along the direction of the row, the opening section being aligned to a position above the mounting terminals, must also be reduced in order to ensure the width of the mounting terminals in the direction of the row and establish electrical conduction with a driver IC. Consequently, a margin of error in positional alignment between the bumps provided on the driver IC and the opening section located above the mounting terminal has become smaller, and there has arisen a problem of a failure to fit the bumps into the opening section when positional displacement having occurred during COG mounting is great. If the bumps fail to fit into the opening section and rest on an insulation film located around the opening section, the following problem will arise.
In mounting of the driver IC by way of the ACF, an overlap area between the bumps and the mounting terminals is reduced, and hence occurrence of a failure of electrical conduction is increased as a result of a decrease in the number of conductive particles contributing to electrical conduction. Moreover, even when electrical conduction were achieved immediately after mounting, a problem of reliability, such as occurrence of an electrical conduction failure, arises in service if the conductive particles in the opening section remain essentially uncollapsed and if the bumps and the mounting terminals cannot be sufficiently bonded through crimping.
Further, in mounting operation for bringing bumps into direct contact with the mounting terminals without involvement of an ACF in order to establish electrical conduction, a contact section between the bumps and the mounting terminal is limited solely to edges of the mounting terminal on the insulation film located around the opening section. Hence, there arises a problem of conduction resistance, namely, an increase in resistance between the bumps and the mounting terminals induced by a significant reduction in contact area.